1. Field of the Invention
The present invention relates to a recording apparatus which forms an image on a recording medium such as a sheet or the like.
2. Related Background Art
In recent years, a decrease in operation sound, as well as improvement in image quality, is desired in a printer. Particularly, in an inkjet recording apparatus having few noise sources at a time of recording, a DC (direct current) motor and a linear encoder are adopted as a driving means to scan a recording head, thereby achieving a low-noise operation. Further, the DC motor and a rotary encoder are being adopted as a driving source to convey sheets. Although an effect of decreasing noise can be expected by only adopting the DC motor, a highly developed stop control technique and machine accuracy are needed to execute highly accurate conveying.
As a method of stopping the DC motor, basically, a method of turning off a power supply of the motor when the rotation of a roller to convey the sheet reaches a target position and thus stopping the motor by inertia is generally known.
To secure stop accuracy using the DC motor, it is necessary and indispensable to lower a prestop speed and eliminate prestop disturbance torque, i.e., to stabilize low-speed driving immediately before the motor stops. That is, a time until the motor stops can be shortened by turning off the power supply of the motor at a constant and sufficiently slow speed, and it becomes difficult to receive disturbance, whereby the stop accuracy of the motor can be secured.
To stabilize the low-speed driving immediately before the motor stops, various manners have been adopted. As a first manner, there is a manner to increase a quantity of information in the low-speed driving immediately before the motor stops and thus improve controllability by using an analog encoder so as to increase resolution of the rotary encoder. As a second manner, there is a manner to sufficiently enlarge the diameter of the rotary encoder (codewheel) as compared with that of the conveying roller to prevent accuracy decrease due to eccentricity of the encoder, and also to increase a peripheral speed of an encoder slit to increase the number of counts of the encoder slit during the low-speed driving immediately before the motor stops, so as to increase the quantity of information and thus improve the controllability.
However, since an extreme torque change is not contained in a torque change of a large period such as a revolution of the conveying roller, the disturbance torque can be eliminated and controlled by lowering to a certain extent the driving speed immediately before the motor stops. However, it is difficult to eliminate small-period disturbance torque, particularly disturbance torque due to a cogging torque ripple of a motor. To cope with this, servo control is executed until the last time that the motor stops by increasing the quantity of information during the low-speed driving immediately before the motor stops so as to suppress small-period torque change and speed change, and also the accuracy is secured by reducing eccentric errors of the conveying roller and the encoder as much as possible so as to tolerate to a certain extent dispersion of the stop accuracy caused by the control.
For this reason, in the conventional method, the analog encoder and the large-diameter codewheel are adopted, thereby increasing cost. Further, in any manner, with respect to the small-period change such as the torque change (or speed change) due to cogging of the motor, the torque (or speed) is forcibly suppressed immediately before the motor stops. Thus, there is a problem that the stop accuracy tends to be influenced and the stop control becomes complicated, because of dispersion caused by mass production regarding the cogging torque ripple of the motor.
Further, for example, control of a pitch in the torque change and the speed change smaller than the period of the cogging torque ripple of the motor, such as an interlock change of a gear and a belt acting as driving transmission means, is more difficult, whereby such an inconvenience can not be solved by the conventional method.
An object of the present invention is to provide a recording apparatus equipped with a conveying configuration in which stop accuracy of a recording medium is not influenced by a torque (speed) ripple of a conveying motor or a transmission means and which is highly accurate and of low cost.
Another object of the present invention is to provide a recording apparatus which comprises a conveying roller for conveying a recording medium, a conveying motor for generating driving force to drive the conveying roller, a driving transmission means for transmitting the driving force of the conveying motor to the conveying roller, a detecting means for detecting a rotation angle of the conveying roller, and a control means for controlling driving and stopping of the conveying roller on the basis of a signal from the detecting means, wherein a conveying quantity of the recording medium at a time of recording operation is an integer multiple of a conveying quantity of the recording medium corresponding to one period of a torque change or a speed change caused by the conveying motor or the driving transmission means.